Sealed System and a Method For Defrosting an Evaporator

ABSTRACT

The present subject matter provides a sealed system for an appliance. The sealed system includes a compressor operable to generate a flow of compressed refrigerant, an evaporator and a drain trough disposed below the evaporator. A bypass conduit fluidly couples a bypass valve and the evaporator. The bypass valve is configured for selectively directing refrigerant from a condenser around an expansion device to the evaporator. A portion of the bypass conduit is positioned at and connected to the drain trough. A related method for defrosting an evaporator is also provided.

FIELD OF THE INVENTION

The present subject matter relates generally to sealed systems for appliances, such as refrigerator appliances, and methods for defrosting evaporators of sealed systems.

BACKGROUND OF THE INVENTION

Refrigerators generally include a cabinet that defines a chilled chamber. The chilled chamber is commonly cooled with a sealed system having an evaporator. One problem frequently encountered with modern refrigerators is inefficient defrosting of the evaporator. For example, when the evaporator is active, frost can accumulate on the evaporator and thereby reduce efficiency of the evaporator. One effort to reduce or eliminate frost from the evaporator has been to utilize a heater to heat the evaporator when the evaporator is not operating.

Suitably defrosting the evaporator with the heater is difficult. For example, heaters can be large energy consumers and can negatively affect the energy efficiency of the refrigerator during long defrosts. In addition, the heater can raise the temperate of the adjacent chilled chamber during long defrosts, and high chilled chamber temperatures can lead to freezer burn and other negative effects. Radiant heaters can also be unsuitable for sealed systems charged with organic, flammable refrigerants due to temperature exposure requirements for such sealed systems. The temperature limits imposed on sealed systems charged with flammable refrigerant can make defrosting an evaporator with a radiant heater impractical.

Accordingly, a sealed system with features for effectively and efficiently defrosting an evaporator would be useful. In addition, a method for effectively and efficiently defrosting an evaporator would be useful.

BRIEF DESCRIPTION OF THE INVENTION

The present subject matter provides a sealed system for an appliance. The sealed system includes a compressor operable to generate a flow of compressed refrigerant, an evaporator and a drain trough disposed below the evaporator. A bypass conduit fluidly couples a bypass valve and the evaporator. The bypass valve is configured for selectively directing refrigerant from a condenser around an expansion device to the evaporator via the bypass conduit. A portion of the bypass conduit is positioned at and connected to the drain trough. A related method for defrosting an evaporator is also provided. Additional aspects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention.

In a first exemplary embodiment, a sealed system for an appliance is provided. The sealed system includes a compressor operable to generate a flow of compressed refrigerant. A condenser is disposed downstream of the compressor such that the condenser receives the flow of compressed refrigerant from the compressor during operation of the compressor. A fan is positioned proximate the condenser and operable to generate a flow of air across the condenser. The sealed system also includes an expansion device and an evaporator. A drain trough is disposed below the evaporator. A bypass valve is disposed downstream of the condenser. A bypass conduit fluidly couples the bypass valve and the evaporator. The bypass valve is configured for selectively directing refrigerant from the condenser around the expansion device to the evaporator. A portion of the bypass conduit is positioned at and connected to the drain trough.

In a second exemplary embodiment, a method for defrosting an evaporator within an appliance is provided. The method includes running a compressor of the appliance during a condenser preheat. A condenser fan of the appliance is deactivated during the condenser preheat such that a temperature of a condenser of the appliance increases while the compressor is running during the condenser preheat. The method also includes actuating a bypass valve of the appliance such that refrigerant from the condenser bypasses an expansion device of the appliance and flows to the evaporator and running the compressor during an evaporator defrost. The temperature of the condenser decreases while the compressor is running during the evaporator defrost.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures.

FIG. 1 is a front elevation view of a refrigerator appliance according to an exemplary embodiment of the present subject matter.

FIG. 2 is schematic view of certain components of the exemplary refrigerator appliance of FIG. 1.

FIG. 3 provides a schematic view of various components of a refrigeration system of the exemplary refrigerator appliance of FIG. 1.

FIG. 4 provides a schematic view of an evaporator and a bypass conduit the exemplary refrigeration system of FIG. 3.

DETAILED DESCRIPTION

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

FIG. 1 depicts a refrigerator appliance 10 that incorporates a sealed refrigeration system 60 (FIG. 2). It should be appreciated that the term “refrigerator appliance” is used in a generic sense herein to encompass any manner of refrigeration appliance, such as a freezer, refrigerator/freezer combination, and any style or model of conventional refrigerator. In addition, it should be understood that the present subject matter is not limited to use in appliances. Thus, the present subject matter may be used for any other suitable purpose, such as in HVAC units.

In the exemplary embodiment shown in FIG. 1, the refrigerator appliance 10 is depicted as an upright refrigerator having a cabinet or casing 12 that defines a number of internal chilled storage compartments. In particular, refrigerator appliance 10 includes upper fresh-food compartments 14 having doors 16 and lower freezer compartment 18 having upper drawer 20 and lower drawer 22. The drawers 20 and 22 are “pull-out” drawers in that they can be manually moved into and out of the freezer compartment 18 on suitable slide mechanisms.

FIG. 2 is a schematic view of certain components of refrigerator appliance 10, including a sealed refrigeration system 60 of refrigerator appliance 10. A machinery compartment 62 contains components for executing a known vapor compression cycle for cooling air. The components include a compressor 64, a condenser 66, an expansion device 68, and an evaporator 70 connected in series and charged with a refrigerant. As will be understood by those skilled in the art, refrigeration system 60 may include additional components, e.g., at least one additional evaporator, compressor, expansion device, and/or condenser. As an example, refrigeration system 60 may include two evaporators.

Within refrigeration system 60, refrigerant flows into compressor 64, which operates to increase the pressure of the refrigerant. This compression of the refrigerant raises its temperature, which is lowered by passing the refrigerant through condenser 66. Within condenser 66, heat exchange with ambient air takes place so as to cool the refrigerant. A condenser fan 72 is used to pull air across condenser 66, as illustrated by arrows A_(C), so as to provide forced convection for a more rapid and efficient heat exchange between the refrigerant within condenser 66 and the ambient air. Thus, as will be understood by those skilled in the art, increasing air flow across condenser 66 can, e.g., increase the efficiency of condenser 66 by improving cooling of the refrigerant contained therein.

An expansion device (e.g., a valve, capillary tube, or other restriction device) 68 receives refrigerant from condenser 66. From expansion device 68, the refrigerant enters evaporator 70. Upon exiting expansion device 68 and entering evaporator 70, the refrigerant drops in pressure. Due to the pressure drop and/or phase change of the refrigerant, evaporator 70 is cool relative to compartments 14 and 18 of refrigerator appliance 10. As such, cooled air is produced and refrigerates compartments 14 and 18 of refrigerator appliance 10. Thus, evaporator 70 is a type of heat exchanger which transfers heat from air passing over evaporator 70 to refrigerant flowing through evaporator 70. An evaporator fan 74 is used to pull air across evaporator 70 and circulated air within compartments 14 and 18 of refrigerator appliance 10.

Collectively, the vapor compression cycle components in a refrigeration circuit, associated fans, and associated compartments are sometimes referred to as a sealed refrigeration system operable to force cold air through compartments 14, 18 (FIG. 1). The refrigeration system 60 depicted in FIG. 2 is provided by way of example only. Thus, it is within the scope of the present subject matter for other configurations of the refrigeration system to be used as well.

FIG. 3 provides a schematic view of various components of refrigeration system 60. As described above, refrigeration system 60 is operable to cool compartments 14 and 18 of refrigerator appliance 10. In such a manner, refrigeration system 60 assists with increasing a storage or shelf life of food items within compartments 14 and 18 of refrigerator appliance 10. Refrigeration system 60 may also include a filter/drier 84 to condition refrigerant within refrigeration system 60. In addition, expansion device 68 is shown as a capillary tube in FIG. 3. A suction line 86 of refrigeration system 60 extends between evaporator 70 and compressor 64 and directs refrigerant from evaporator 70 to compressor 64 during operation of compressor 64. Suction line 86 is coupled to the capillary tube in order to provide heat transfer between refrigerant entering evaporator 70 from the capillary tube and refrigerant returning to compressor 64 from evaporator 70 via suction line 86.

During operation of refrigeration system 60, water vapor in compartments 14 and 18 of refrigerator appliance 10 may condense onto evaporator 70 and form frost buildup on evaporator 70. Overtime, frost accumulation on evaporator 70 can negatively affect performance of evaporator 70. Thus, refrigeration system 60 includes features for defrosting evaporator 70. In particular, refrigeration system 60 includes features for fully and/or efficiently defrosting evaporator 70 relative to known systems that expose evaporators to radiant heating elements during defrosts. Such features of refrigeration system 60 are discussed in greater detail below in the context of FIG. 3.

As shown in FIG. 3 and as discussed above, refrigeration system 60 includes compressor 64, condenser 66, expansion device 68 and evaporator 70 that are connected to each other in a loop in order to execute a known vapor compression cycle for cooling air. Refrigeration system 60 also includes a bypass valve 80 and a bypass conduit 82 that interrupt the normal refrigerant operating loop of refrigeration system 60 during a defrosting operation of refrigeration system 60.

Bypass valve 80 is disposed downstream of condenser 66. Thus, refrigerant from condenser 66 flows to bypass valve 80 within refrigeration system 60 during operation of compressor 64. As an example, bypass valve 80 may be a two-way valve, such as a two-way solenoid valve. As another example, bypass valve 80 may be a three-way valve, such as a three-way solenoid valve. Bypass conduit 82 fluidly couples bypass valve 80 and evaporator 70 such that refrigerant at bypass valve 80 may flow through bypass conduit 82 to evaporator 70. As an example, bypass conduit 82 may be (e.g., aluminum or copper) tubing or piping that extends from bypass valve 80 to an inlet of evaporator 70. Thus, bypass valve 80 and evaporator 70 may be in direct fluid communication with each other via bypass conduit 82.

Bypass valve 80 is selectively adjustable between a normal operating configuration and a bypass operating configuration. In the normal operating configuration, refrigerant from condenser 66 flows through bypass valve 80 to expansion device 68 during operation of compressor 64. Thus, refrigerant flows through refrigeration system 60 in the manner described above with reference to FIG. 2 when bypass valve 80 is in the normal operating configuration such that refrigeration system 60 operates to cool compartments 14 and 18 of refrigerator appliance 10. Conversely, refrigerant from condenser 66 flows through bypass valve 80 to evaporator 70 during operation of compressor 64 in the bypass operating configuration. Thus, refrigerant from condenser 66 bypasses expansion device 68 in the bypass operating configuration such that refrigeration system 60 does not operate to cool compartments 14 and 18 of refrigerator appliance 10. By actuating from the normal operating configuration to the bypass operating configuration, bypass valve 80 may assist with implementing a defrost cycle of refrigeration system 60. In the bypass operating configuration, a mass flow rate of refrigerant through refrigeration system 60 may be greater than when bypass valve 80 is in the normal operating configuration, e.g., due to removal of expansion device 68 from the flow path of refrigerant in refrigeration system 60. In turn, heat transfer in evaporator 70 may increase in direct proportion to the mass flow increase, e.g., and thereby improve the efficiency of defrost cycles, as described in greater detail below.

Refrigerant at an inlet of evaporator 70 is hotter when bypass valve 80 is in the bypass operating configuration compared to when bypass valve 80 is in the normal operating configuration. Thus, refrigerant delivered to evaporator 70 via bypass conduit 82 may flow into evaporator 70 and heat evaporator 70 after shifting bypass valve 80 from normal operating configuration to the bypass operating configuration. By heating evaporator 70, the refrigerant within evaporator 70 melts ice on an outer surface of evaporator 70 and thereby defrosts evaporator 70. Thus, bypass valve 80 and bypass conduit 82 may assist with defrosting evaporator 70 by bypassing refrigerant flow around expansion device 68 and delivering refrigerant that is hotter than the freezing temperature of water into evaporator 70. As an example, when bypass valve 80 is in the bypass operating configuration, refrigerant entering evaporator 70 from bypass conduit 82 may have a temperature no less than sixty degrees Celsius (60° C.). Heat may be evenly distributed through evaporator 70 via refrigerant during defrost cycles when bypass valve 80 is in the bypass operating configuration. In contrast, standard defrosting methods utilizing radiant heating elements adjacent an associated evaporator heat only areas of the associated evaporator that are in line-of-sight of the radiant heating element or in contact with the radiant heating element.

As shown in FIG. 3, a drain trough 90 is disposed, e.g., directly, below evaporator 70. Drain trough 90 collects liquid runoff from evaporator 70 during defrost cycles and directs the liquid runoff away from evaporator 70. In such a manner, drain trough 90 may assist with removing liquid water from compartments 14 and 18 during defrost cycles. Drain trough 90 may be made of any suitable material, e.g., metal or plastic. From drain trough 90, the liquid runoff from evaporator 70 may be directed to any suitable location, such as a drain line out of refrigerator appliance 10 or to an open topped evaporation pan 92 below condenser 66. Thus, a drain line may extend from drain trough 90 to an exterior drain or to evaporation pan 92 to dispose of the liquid runoff from evaporator 70.

Drain trough 90 may be sized to assist with collecting liquid runoff from evaporator 70. For example, an area or footprint of drain trough 90, e.g., in a plane that is perpendicular to vertical, may be larger than a corresponding area or foot print of evaporator 70. In particular, drain trough 90 defines a length L. The length L of drain trough 90 may be larger than a corresponding length of evaporator 70 such that drain trough 90 is larger than and extends past evaporator 70.

At least a portion of bypass conduit 82 may also be positioned at and connected to drain trough 90. Thus, bypass conduit 82 and drain trough 90 may be in conductive thermal communication with each other. As an example, a portion of bypass conduit 82 may be brazed or soldered to drain trough 90. As another example, a portion of bypass conduit 82 may be clipped, fastened, adhered or otherwise mounted to drain trough 90. By connecting bypass conduit 82 to drain trough 90, heat transfer between bypass conduit 82 and drain trough 90 may assist with melting ice within drain trough 90 thereby assisting with proper operation of drain trough 90. In certain exemplary embodiments, bypass conduit 82 is positioned on and contacts drain trough 90 along the length L of drain trough 90 in order to increase heat transfer between bypass conduit 82 and drain trough 90.

As discussed above, bypass conduit 82 may be tubing or piping. In certain exemplary embodiments, bypass conduit 82 may be metal tubing, such as copper or aluminum tubing, having a circular cross-section along a length of the metal tubing. Thus, bypass conduit 82 may define an internal diameter, and the internal diameter of bypass conduit 82 may be constant. The internal diameter of bypass conduit 82 may be selected to match adjacent sections of tubing or piping within refrigeration system 60. For example, the internal diameter of bypass conduit 82 may be selected to match an exit line of condenser 66 and/or an inlet line of evaporator 70. In such a manner, a pressure drop of refrigerant within bypass conduit 82 between condenser 66 and evaporator 70 when bypass valve 80 is in the bypass operating configuration may be limited or reduced.

Refrigeration system 60 also includes an electric heating element 94, such as a resistance heating element, in certain exemplary embodiments. Heating element 94 is positioned on and/or mounted to bypass conduit 82. Thus, when activated, heating element 94 may heat bypass conduit 82 and refrigerant within bypass conduit 82. In certain exemplary embodiments, heating element 94 may be encased within foam insulation of refrigerator 10, e.g., in a wall of casing 12. Thus, heating element 94 may be spaced apart from evaporator 70, e.g., such that refrigeration system 60 does not include an electric heating element disposed at or exposed to an outer surface of evaporator 70. Such positioning of heating element 94 can allow heating element 94 to increase a temperature of refrigerant entering evaporator 70 during defrost cycles while also limiting an operating temperature of heating element 94, as discussed in greater detail below.

Refrigeration system 60 may be charged with a flammable refrigerant, such as a flammable alkane, hydrocarbon or organic compound. As another example, the flammable refrigerant may be R600a. When charged with flammable refrigerant, a maximum operating temperature of components within refrigerator appliance 10 may be limited to no more than a maximum temperature, e.g., six hundred and eighty degrees Fahrenheit (680° F.). By positioning heating element 94 in contact with bypass conduit 82, heat transfer between heating element 94 and bypass conduit 82 may be both radiant heat transfer and conductive heat transfer, and the maximum operating temperature of heating element 94 may be no greater than six hundred and eighty degrees Fahrenheit while heating element 94 operates to heat refrigerant entering evaporator 70 during defrost cycles. In addition, positioning heating element 94 within foam insulation may remotely position heating element 94 relative to evaporator 70 such that heating element 94 is remotely positioned relative to a space where refrigerant can collect within refrigerator 10.

Components of refrigeration system 60 may also be operated to assist defrosting of evaporator 70. For example, condenser fan 72 may be configured to deactivate whenever bypass valve 80 is in the bypass operating configuration and bypass valve 80 directs refrigerant from condenser 66 around expansion device 68 to evaporator 70. In particular, a defrost cycle according to the present subject matter may include a condenser preheat portion and an evaporator defrost portion, e.g., that are performed sequentially. Compressor 64 runs during the condenser preheat portion of the defrost cycle. In addition, bypass valve 80 is in the normal operating configuration and condenser fan 72 is deactivated during the condenser preheat portion of the defrost cycle. Thus, a temperature of condenser 66 increases while compressor 64 is running during the condenser preheat. By deactivating condenser fan 72 and reducing convective heat transfer between condenser 66 and ambient air about condenser 66, condenser 66 may function as a thermal capacitor during the condenser preheat portion of the defrost cycle and thereby provide thermal energy to other components of refrigeration system 60 during later portions of the defrost cycle, as discussed in greater detail below.

After the condenser preheat portion of the defrost cycle, bypass valve 80 shifts or actuates from the normal operating configuration to the bypass operating. Thus, after increasing the temperature of condenser 66 during the preheat portion of the defrost cycle, bypass valve 80 actuates to the bypass operating configuration such that refrigerant from condenser 66 bypasses expansion device 68 and flows to evaporator 70 via bypass conduit 82.

After actuating bypass valve 80 to the bypass operating configuration, compressor 64 runs during the evaporator defrost portion of the defrost cycle. As discussed above, the temperature of condenser 66 increases while compressor 64 is running during the condenser preheat. Conversely, the temperature of condenser 66 decreases while compressor 64 is running during the evaporator defrost portion of the defrost cycle. In particular, heat transfer between condenser 66 and refrigerant within condenser 66 may increase the temperature of refrigerant exiting condenser 66, and the heated refrigerant from condenser 66 may flow to evaporator 70 via bypass conduit 82 in order to defrost evaporator 70, as discussed above. In such a manner, the mass of condenser 66 may provide thermal storage for later portions of the defrost cycle. Condenser fan 72 may also be deactivated during the evaporator defrost portion of the defrost cycle in order to limit heat transfer between condenser 66 and ambient air about condenser 66. Further, heating element 94 may be activated during the evaporator defrost portion of the defrost cycle in order to heat refrigerant within bypass conduit 82.

Defrosting evaporator 70 in the manner discussed above can have numerous potential benefits. For example, evaporator 70 may be defrosted more efficiently using refrigerant from condenser 66 compared to systems using radiant heating elements to defrost an evaporator. In addition, heating element 94 may be positioned at and operate in an area with reduced risk for flammability of an organic compound. Further, defrosting without an exposed radiant heating element in freezer compartment 18 can reduce or eliminate freezer burn on food items stored in the freezer compartment 18.

FIG. 4 provides a schematic view of evaporator 70 and bypass conduit 82. As may be seen in FIG. 4, evaporator 70 may include a conduit 100 that extends, e.g., longitudinally, between an inlet 102 and an outlet 104. Conduit 100 may be any suitable tubing, piping, etc. for containing a flow of refrigerant. As a particular example, conduit 100 may include a continuous piece of aluminum or copper tubing that extends from inlet 102 of conduit 100 to outlet 104 of conduit 100. When bypass valve 80 is in the bypass operating configuration, a flow of refrigerant within refrigeration system 60 enters conduit 100 at inlet 102 of conduit 100. Conduit 100 guides or directs the flow of refrigerant through conduit 100 to outlet 104 of conduit 100. From outlet 104, the flow of refrigerant may return to compressor 64. Bypass conduit 82 may be coupled to conduit 100 at or adjacent inlet 102 of conduit 100.

Conduit 100 also extends between or includes a top portion 103 and a bottom portion 105. Top portion 103 and bottom portion 105 of conduit 100 may be spaced apart from each other, e.g., along a vertical direction V. In particular, top portion 103 of conduit 100 may be positioned above bottom portion 105 of conduit 100, e.g., along the vertical direction V. Inlet 102 and outlet 104 of conduit 100 may both be positioned at or adjacent top portion 103 of conduit 100.

Conduit 100 may be bent or formed into any suitable shape. For example, as shown in FIG. 4, conduit 100 may be bent or formed to include a serpentine segment or section 108 and a linear segment or section 109. Linear section 109 of conduit 100 may be disposed or formed downstream of serpentine section 108 of conduit 100 relative to the flow of refrigerant through conduit 100. Serpentine section 108 of conduit 100 includes a plurality of bends. Thus, refrigerant flowing through serpentine section 108 of conduit 100 may change directions multiple times. Serpentine section 108 of conduit 100 may be provided or formed in order to permit conduit 100 to have a long length between inlet 102 and outlet 104 of conduit 100 while also reducing a foot print of evaporator 70 within refrigerator 10. Linear section 109 of conduit 100 extends from bottom portion 105 of conduit 100 to top portion 103 of conduit 100. Thus, after flowing through serpentine section 108 of conduit 100 from top portion 103 to bottom portion 105 of conduit 100, the refrigerant within conduit 100 may flow back towards top portion 103 of conduit 100 (e.g., and outlet 104) via linear section 109 of conduit 100.

Conduit 100 may also include a pair of jumper tubes, each positioned at a respective one of inlet 102 and outlet 104 of conduit 100. The jumper tubes may assist with coupling evaporator 70 to other components of refrigeration system 60. For example, as discussed above, conduit 100 may include aluminum tubing between inlet 102 and outlet 104 of conduit 100. In contrast, the jumper tubes may be copper tubing. Copper tubing can be significantly easier to join together with solder compared to aluminum tubing. Thus, the jumper tubes may facilitate connection of evaporator 70 into refrigeration system 60 by providing a connection point to adjacent tubing. For example, bypass conduit 82 may be coupled to the jumper tube at inlet 102 of conduit 100.

Conduit 100 also defines an outer surface 106. A spine fin heat exchanger 110 is wound onto conduit 100 at outer surface 106 of conduit 100. In particular, spine fin heat exchanger 110 may form a helix on outer surface 106 of conduit 100. Spine fin heat exchanger 110 assist with heat transfer between air passing over evaporator 70 and refrigerant flowing through conduit 100, e.g., by increasing a heat exchange surface exposed to the air about evaporator 70.

As shown in FIG. 4, bypass conduit 82 includes a first segment or section 120 and a second segment or section 122. First section 120 of bypass conduit 82 is positioned on and/or mounted to drain trough 90. Conversely, second section 122 of bypass conduit 82 is positioned above drain trough 90, e.g., along the vertical direction V. In particular, second section 122 of bypass conduit 82 may span or be positioned within a gap between evaporator 70 and drain trough 90, e.g., along the vertical direction V. Thus, second section 122 of bypass conduit 82 may be positioned between evaporator 70 and drain trough 90, e.g., along the vertical direction V. Second section 122 of bypass conduit 82 may assist with limiting ice accumulation between evaporator 70 and drain trough 90.

Plate fins 124 may be mounted to bypass conduit 82 at second section 122 of bypass conduit 82. For example, second section 122 of bypass conduit 82 may be bent into a serpentine pattern, and plate fins 124 may extend between windings or coils of second section 122 of bypass conduit 82. Plate fins 124 assist with heat transfer between air passing over bypass conduit 82 and refrigerant flowing through second section 122 of bypass conduit 82, e.g., by increasing a heat exchange surface exposed to the air about bypass conduit 82. Plate fins 124 also may further assist with limiting ice accumulation between evaporator 70 and drain trough 90.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

What is claimed is:
 1. A sealed system for an appliance, comprising: a compressor operable to generate a flow of compressed refrigerant; a condenser disposed downstream of the compressor such that the condenser receives the flow of compressed refrigerant from the compressor during operation of the compressor; a fan positioned proximate the condenser and operable to generate a flow of air across the condenser; an expansion device; an evaporator; a drain trough disposed below the evaporator; a bypass valve disposed downstream of the condenser; and a bypass conduit fluidly coupling the bypass valve and the evaporator, the bypass valve configured for selectively directing refrigerant from the condenser around the expansion device to the evaporator via the bypass conduit, a portion of the bypass conduit positioned at and connected to the drain trough.
 2. The sealed system of claim 1, wherein the drain trough defines a length, the bypass conduit contacting the drain trough along the length of the drain trough.
 3. The sealed system of claim 1, wherein the bypass conduit defines a constant internal diameter.
 4. The sealed system of claim 1, wherein the fan is configured to deactivate whenever the bypass valve directs refrigerant from the condenser around the expansion device to the evaporator.
 5. The sealed system of claim 1, wherein the sealed system is charged with a flammable refrigerant.
 6. The sealed system of claim 5, wherein the flammable refrigerant comprises a flammable alkane, hydrocarbon or organic compound.
 7. The sealed system of claim 1, further comprising an electric heating element mounted to the bypass conduit.
 8. The sealed system of claim 7, wherein the electric heating element is encased within foam insulation.
 9. The sealed system of claim 1, wherein the sealed system does not include an electric heating element disposed at an outer surface of the evaporator.
 10. A method for defrosting an evaporator within an appliance, comprising: running a compressor of the appliance during a condenser preheat, a condenser fan of the appliance being deactivated during the condenser preheat such that a temperature of a condenser of the appliance increases while the compressor is running during the condenser preheat; actuating a bypass valve of the appliance such that refrigerant from the condenser bypasses an expansion device of the appliance and flows to the evaporator; and running the compressor during an evaporator defrost, the temperature of the condenser decreasing while the compressor is running during the evaporator defrost.
 11. The method of claim 10, wherein the condenser fan is deactivated during the evaporator defrost.
 12. The method of claim 10, wherein a bypass conduit fluidly coupling the bypass valve and the evaporator is connected to a drain trough disposed below the evaporator.
 13. The method of claim 12, wherein a portion of the bypass conduit extends along a length of the drain trough.
 14. The method of claim 12, further comprising operating an electric heating element mounted to the bypass conduit during the evaporator defrost.
 15. The method of claim 14, wherein the electric heating element is encased within foam insulation.
 16. The method of claim 10, wherein the refrigerant is a flammable refrigerant.
 17. The method of claim 16, wherein the flammable refrigerant comprises a flammable alkane, hydrocarbon or organic compound. 